How to convert a SQL Server cursor to MySQL equivalent

问题

How can I convert the procedure below to MySQL format?

Here is the piece to be converted:

DECLARE @CurrentFirstName varchar(300)
DECLARE @CurrentAge INT

DECLARE CursorName CURSOR FAST_FORWARD FOR 
    SELECT Firstname,Age 
    FROM Customers

OPEN CursorName
FETCH NEXT FROM CursorName INTO @CurrentFirstName, @CurrentAge

WHILE @@FETCH_STATUS = 0
BEGIN
      IF @AGE>60 /*this is stupid but we can apply any complex condition here*/ BEGIN
    insert into ElderCustomers values (@CurrentFirstName,@CurrentAge)
      END


    FETCH NEXT FROM CursorName INTO @CurrentFirstname,@CurrentAge
END

CLOSE CursorName
DEALLOCATE CursorName

Sorry in advance if there is something wrong above

回答1:

The MySQL equivalent would be something like this:

BEGIN
  DECLARE CurrentFirstName VARCHAR(300);
  DECLARE CurrentAge INT;
  DECLARE done INT DEFAULT FALSE;
  DECLARE CursorName CURSOR FOR
    SELECT FirstName, Age FROM Customers;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
  OPEN CursorName;
  myloop: LOOP
    FETCH CursorName INTO CurrentFirstName, CurrentAge;
    IF done THEN
      LEAVE myloop;
    END IF;
    IF CurrentAge > 60 THEN
      insert into ElderCustomers values (CurrentFirstName,CurrentAge);
    END IF;
  END LOOP;
  CLOSE CursorName;
END;

The big difference is in the loop, using the CONTINUE HANDLER to set a flag when there are no more rows to fetch, and exiting the loop when the flag is set. (That looks ugly, but that's the way it's done in MySQL.)

This example begs the question why this isn't written (more efficiently, in both SQL Server and MySQL) as:

INSERT INTO ElderCustomers (FirstName, Age)
SELECT FirstName, Age
  FROM Customers
 WHERE Age > 60

来源：https://stackoverflow.com/questions/17871926/how-to-convert-a-sql-server-cursor-to-mysql-equivalent

标签

mysql

sql-server-2008-r2

cursor